Vegetables are a wonderful and mysterious kingdom, inhabited by an alien chemistry that has varied effects on our animal bodies. Many vegetable cells contain chlorophyll, while animal red blood cells have hemoglobin. Vegetable cells have both a cell wall and a membrane, while animal cells have only a membrane, and since humans cannot digest cell walls, vegetables make wonderful roughage. OTOH, no vegetable cells contain Vitamin B12, which is an essential cofactor in the production of DNA in animal cells. And if you eat a random animal, the odds are that you will not get sick, while eating a random vegetable is fraught with dangerous possibilities. Some vegetables are processed to make useful medicines: opium, marijuana, alcohol, aspirin, chocolate, tea, coffee, artemisin, quinine, taxol, digitalis, and some contain dangerous poisons: opium, alcohol, digitalis, mistletoe, oleander, some mushrooms, nightshade, tobacco, LSD, nutmeg, peyote, cocaine, jimson weed, manicheel. As far as I am aware, the only addicting foods that can cause dependency and lead to severe withdrawal effects are from the vegetable kingdom (e.g. alcohol and opium/heroin). As an example of how unknowing we can be, when Bayer patented heroin, aka diacetyl morphine, it was touted and sold OTC as non-addictive morphine (and at the same time, in the 1900's, aspirin was available by Rx only).
The benefits of coffee are many and varied, which is not to say that too much cannot produce unwanted and unwelcome side effects. Some of the benefits have been demonstrated in humans, while others have only helped laboratory rats. Some people will have a reaction similar to drinking coffee when they ingest chocolate, because theobromine is a xanthine, as is caffeine. PubMed is a website operated by the National Library of Medicine, and if you have questions about any of the studies I quote in abbreviated form, you can find an abstract of the pertinent clinical article and a reference to the whole article at this site.
The following is a list of some of the reputed benefits of coffee (caffeine) ingestion. I can vouch for some of them, because we all took No-Doz in college and medical school when pulling an all-nighter studying for a test, and one No-Doz has the caffeine equivalent of two cups of coffee. And whether it worked or not, studies have shown that if you think you are drinking coffee, you show some of the benefits. I should mention that the caffeine in coffee starts to be absorbed 15 minutes after ingestion, reaches a peak blood level after 45 minutes, and its half-life is 6 hours. Ingestion of the antibiotic Levaquin or the antidepressant Luvox prolongs its half-life and significantly increases its peak level by competitive inhibition of the degradation of caffeine by your liver.
1) Reduces the chance of developing adult-onset diabetes (greater effect in women than men)
2) Reduces the appetite
3) May reduce your chance of developing Parkinson's Disease. The confounding factor here is that smoking definitely reduces your chance of developing Parkinson's Disease due to the nicotine receptors in the brain, and more coffee drinkers smoke than do non-coffee drinkers.
4) Improves motor skills in patients with Parkinson's Disease.
5) Enhances the analgesic effect of all pain medicines.
6) Reduces depression, and enhances a feeling of well-being
7) May help dilate the bronchioles in asthmatic patients.
8) Improves the on-the-job efficiency of shift workers who have staggered sleep schedules.
9) Decreases mental fatigue from sleepiness.
10) Extends the time to physical fatigue from exercise.
11) Instant memory ability peaks in the morning and slowly decreases throughout the day. Morning coffee blocks this effect.
12) Enables functioning at a higher work load than usual.
13) Some studies show a quickening of brain cell synapse time, mostly in rats.
14) Improves eye-hand coordination.
15) Decreases the risk of some cancers.